I’m expecting that any page accessed from France will serve its “ug1.html” variation. And it does serve the right html file but it also make my assets inaccessible. Could it be that whatever/style.css is also impacted by the redirect rule?
Because my understanding is that direct access to file will never be matched unless you add a ! to the code (/* :splat/ug1.html 200! Country=fr)

you’d want at least to use /:splat/ug1.html (note the leading /) for consistency.

The behavior you’re seeing where the language redirect is treated as forced is a bug, but not one we’re likely to fix soon based on what I’ve seen of our roadmap. You’ll need to mirror your assets into the /whatever/ directory to work around it for now. Sorry, I know that is rather inelegant

I’ve attached this thread to the bug report so we can let you know if we do later fix the bug.